Transparent polyolefin films of high modulus and clarity

ABSTRACT

INCREASED STIFFNESS AND BETTER CLARITY OF POLYMERIC FILMS CAN BE OBTAINED BY COMPRESSION ROLLING RELATIVELY THICK FILMS OF THE POLYMERS, PROVIDED THAT THE FILMS ARE COATED (AT THE JUNCTURE OF THE ROLLS WITH THE FILM) WITH ENOUGH LIQUID &#34;LUBRICANT&#34; TO FORM A &#34;HYDRODYNAMIC WEDGE&#34; IN THE NIP AREA. FILMS HAVING HIGHER MODULUS AND GREATER CLARITY (THAN COULD OTHERWISE BE PRODUCED) CAN BE MANUFACTURED BY THIS PROCESS. POLYOLEFIN FILMS HAVING SUCH HIGHER MODULUS PLUS EXCELLENT CLARITY (LESS THAN 3% HAZE) ARE CLAIMED.

June 27, 1972 WILLIAMS, JR ETAL Re. 27,404

TRANSPARENT POLYOLEFIN FILMS OF HIGH MODULUS AND CLARITY Original FiledJuly 14, 1966 ROBERT E W/LL/AM.S,JR.

RICHARD H. .15 KS 523 BY AM? A TTOR/VEYS United States Patent OfliceReissued June 27, 1972 27,404 TRANSPARENT POLYOLEFIN FILMS OF HIGHMODULUS AND CLARITY Robert F. Williams, Jr., Webster, and Richard H.Jenks, Rome, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y.

Original No. 3,503,843, dated Mar. 31, 1970, Ser. No. 683,064, Oct. 16,1967, which is a division of Ser. No. 565,305, July 14, 1966, which is acontinuation-in-part of Ser. No. 197,217, May 7, 1962, which is acontinuation-in-part of Ser. No. 9,567, Feb. 18, 1960, Ser. No. 16,208,Mar. 21, 1960, and Ser. No. 30,324, May 19, 1960. Application Ser. No.16,208 is a continuation-inpart of Ser. No. 833,666, Aug. 10, 1959,which is a continuation-in-part of Ser. No. 706,626, Jan. 2, 1958.Application for reissue July 31, 1970, Ser. No. 59,959

Int. Cl. B3211 27/32 US. Cl. 161-165 8 Claims Matter enclosed in heavybrackets appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE Increased stiffness and better clarity ofpolymeric films can be obtained by compression rolling relatively thickfilms of the polymers, provided that the films are coated (at thejuncture of the rolls with the film) with enough liquid lubricant toform a hydrodynamic wedge in the nip area. Films having higher modulusand greater clarity (than could otherwise be produced) can bemanufactured by this process. Polyolefin films having such highermodulus plus excellent clarity (less than 3% haze) are claimed.

This application is a division of United States patent application Ser.No. 565,305, filed July 14, 1966 (now abandoned), which in turn was acontinuation-in-part of United States patent application Ser. No.197,217, filed May 7, 1962 (now abandoned), which in turn was acontinuation-in-part of United States patent applications Ser. No.9,567, filed Feb. 18, 1960 (now abandoned); Ser. No. 16,208, filed Mar.21, 1960 (now abandoned); and Ser. No. 30,324, filed May 19', 1960 (nowabandoned). Application Ser. No. 16,208 was a continuationin-part of US.patent application Ser. No. 833,666 filed Aug. 10, 1959 (now abandoned)which, in turn, was a continuation-in-part of US. patent applicationSer. No. 706,626, filed Jan. 2, 1958 (now abandoned). This applicationis a reissue of US. Patent 3,503,843, issued Mar. 3], I 970.

This invention relates to the fabrication of strong, clear, transparentfilm in sheets from organic polymeric thermoplastic film.

Sheeting made from synthetic organic thermoplastic materials has foundconsiderable utility for packaging purposes, photographic film base, andthe like. However, it has been desired to have improved stiffness andclarity for many of these polymeric films. In addition, it has beendesirable to incorporate into the polymeric materials one or more of alarge number and types of additives such as stabilizers, antioxidants,ultraviolet absorbers, slip agents, antiblocking agents,moisture-proofing agents, and the like.

Various methods are known for improving the physical characteristics ofpolymeric film; for instance, the material may be extruded into a quenchbath. Some films may be stretched in one or both directions and stillothers may be calendered using heated rolls above the softeningtemperature of the polymeric film. However, the clarity of some of thesefilms has not been satisfactory for many purposes, and it has beendesirable to find a method of improving the clarity. Moreover, thestretching method tends to enlarge any pin holes or voids which may beexisting in the polymeric film as originally prepared. This furtherdecreases the moisture-barrier properties of the film and decreases itsusefulness for packaging purposes.

The addition of additives to polymeric materials usually occurs prior tothe extrusion step or solution step if the film is to be cast. Theadditive is added to the polymer and incorporated throughout theresulting structure. Therefore, it is necessary to know before preparingthe initial film what additive or additives are to be added to thepolymeric film. This necessarily reduces the ability of the manufacturerto add additives once a film strip has been prepared, and it has beendesired to find a method of adding various agents to the film dependingupon its ultimate use after the film has been extruded or cast.Moreover, it has been determined that most of the additives in polymericfilm exert their beneficial effect at the surface of the film.Accordingly, it is preferable to have the additive located solely at thesurface of the film if this were conveniently possible, not only toincrease the effectiveness of the additive but to decrease the quantityof the additive required which would not be needed in the interior ofthe film.

We have found a method of compression rolling polymeric film formed byeither extrusion or cast-coating which improves (1) the clarity of thefilm, (2) the moisture-barrier properties, (3) the stiffness as measuredby Youngs modulus, and (4) the tensile strength as well as othermechanical properties. We have also found a method of incorporatingadditives in the surface during the compression-rolling operation.

One object of this invention is to provide a method for compressionrolling polymeric materials at lower pressures and/or temperatures thanused previously for obtaining the same thickness reduction. Anadditional object is to provide a process of compression rollingpolymeric materials using lubricants. A further object of this inventionis to provide a method of improving the crystalline structure ororientation of the molecules in polymeric films. Another object is toprovide polymeric materials which have additives incorporated in thesurface of the polymeric films. An additional object is to provide amethod of incorporating various additives into the surface of polymericfilms.

The above objects are obtained by compression rolling the polymeric filmunder specific operating conditions. The polymeric sheeting is passedbetween rollers having a pressure sufficient to decrease the film toone-half to onetenth in thickness. A lubricant is used on the polymericfilm as it passes through the nip between the two rollers. Thislubricant can be applied to either the polymeric sheeting directly'orplaced on the rollers so it is transferred to the polymer as it passesbetween the rollers. The temperature of the pressure rollers depends onthe density and the softening temperature of the polymer. For mostpolymers, the temperature can be at room temperature, but it may bevaried from 40-300 F. depending upon the polymer.

By a lubricant is meant a liquid or material that acts as a liquid inthe area where pressure from the rolls is applied to the film. Thelubricant in this case acts to form a full or partial fluid film betweenthe roll and the polymeric film. Thus, the roll surface and polymericfilm are separated by the liquid lubricant which prevents contact andincreases mobility as the film enters the nip. This fiuid film formationis based on the hydrodynamic theory for bearings. The theory andexperimental data prove that by applying a copius supply of lubricantwith the proper geometry and sufficient speed a hydrodynamic wedge or mis formed. This results in effectively reducing the nip load area whichresults in higher unit stresses for a ven load. Thus the effective peakpressure generated in e nip is increased by the hydrodynamic effect overthat hich would be expected by elastic theory.

This type of lubrication deviates from the common or nventional boundarytype where a lubricant, liquid or lid, is impregnated or applied to thepolymeric surface. Jnventional lubrication is based on the theory ofboundy lubrication which effectively reduces friction in the nge ofmu=.2 or .3 to m;r=.l to .15. The claimed iique method of producing ahydrodynamic film results coefficient of friction values in the order ofm .=.00l. 1is reduction in friction has minor effect in reducing dryidding and heat generation. The major effect of using a 'drodynamicwedge is in its ability to effectively reduce e area under load, thuswith the same total load create much higher unit pressure.

In the event that water is used as a lubricant, it is deable to add awetting agent such as Aerosol OT which dioctyl sodium sulfosuccinate. Asufiicient amount of e lubricant is used to cover the surface of thepolymer it passes between the rolls. The application may be by ray,wick, immersion coating, etc. Methods of insuring rface coverage may beused such as air knife, bar, wick, d the like. The lubricant which maybe used must be inert material which will not adversely affect thefinled product, and it should preferably wet the surface tficiently tocover the surface at the point of pressure [ring the compression-rollingoperation. The additives, if sired, are incorporated into the lubricantand the luicant is chosen so that it will form a solution of the ditivein our preferred embodiment, although emulsions suspensions can be used,particularly when the additive an inorganic solid such as silica or thelike.

In the event that a particular organic chemical were be used as anadditive, it might be dissolved in a solvent ch as ethyl alcohol or thelike and used as a lubricant. irious solvents may be combined to form asuitable bricating mixture which will satisfactorily dissolve thelditive and incorporate it into the surface of the film.

A group of antioxidant compounds suitable for use additives ofpolyolefins according to our invention inide phenolic compounds. Thisgroup includes: phenol, kylphenols, such as2,4-dimethyl-6-tertiarybutylphenol .d 2,6-ditertiarybutyl4-methylphenol; a-naphthol; dihyoxynaphthalenes, such as 1,5- and1,7-dihydroxynaphalenes and the monoalkylethers thereof; 1-hydroxy-4-oxy-5,8-dihydronaphthalene; catechol and alkyl cateols includingnordihydroguiairetic acid; dihydroxybenne, such as hydroquinone, andalkyldihydroxybenzenes .d monoalkylethers thereof, such as2-tertiarybutyl-4-meoxyphenyl; trihydroxybenzenes such as pyrolgalloland rylpyrogallols; alkyl gallates; 2,2-dimethyl-5-hydroxy-6-rtiarybutylcoumaran; and 2,2-dimethyl-6-hydroxy-7-tertrybutylcoumaran.It can be seen that the phenolic comunds may be mono or polynuclear andmay contain one more hydroxyl groups (that is to say they be monoorllyhydric phenols) and substituted hydroxy groups such alkoxysubstituents.

Another group of organic antioxidant compounds parularly suitable foradding in accordance with this inntion comprises p-substituted anilineswherein the pbstituent is selected from the group consisting of hyoxyl,amino and alkylamino radicals, e.g., p-aminoilines andp-hydroxyanilines. This group of compounds 1y be further classified asp-substituted-N-alkylanilines lerein the p-substituent is selected fromthe group conting of hydroxyl, amino and alkylamino radicals suchp-amino-N-alkylanilines; p-alkylamino-N-alkylanilines; dhydroxy-N-alkylanilines. This group of compounds inldesp-sec-butylamino-N-sec-butyl-aniline, p-hydroxy-N- :thylaniline,p-n-butylamino-N-n-butyl-aniline, and o-:thyl-p-sec-butylamino-N-sec-butylaniline.

The foregoing and similar organic antioxidant compounds may be usedindividually, and also two or more of these organic compounds may beused together.

The following may also be used: synergistic stabilizer combinationcomprising a 4-alkoxy-2-hydroxy-benzophenone and a diester ofbeta,beta-thiodipropionic acid as disclosed in U.S. Pat. 2,972,597,issued Feb. 21, 1961 and U.S. Pat. 2,861,053, issued Nov. 18, 1958; asynergistic stabilizer combination comprising a4-alkoxy-2-hydroxybenzophenone and a zinc N,N-dialkyldithiocarbamate asdisclosed in U.S. Pat. No. 2,972,597, issued Feb. 21, 1961; asynergistic stabilizer combination comprising a 4-higheralkoxy-2-hydroxybenzophenone and an alkylene-bis-phe- 1101 of the groupconsisting of 2,2-methylene-bis(4-methyl-6-(1- methylcyclohexyl)phenol)and 4,4'-ethylene-dioxybis(Z-tertiarybutylphenol) as described in U.S.Pat. 2,976,260, issued Mar. 21, 1961; a synergistic stabilizercombination comprising a 4-alkoxy-2-hydroxybenzophenone andN,N'-diphenyl-p-phenylenediamine as described in U.S. Pat. 2,947,721,issued Aug. 2, 1960; a stabilizer combination comprising resorcinolmonobenzoate and 2,2'-methylenebis(6-tertiarybutyl-p-cresol) asdescribed in U.S. Pat. 2,983,709, issued May 9, 1961; a stabilizercombination comprising a tris-(dialkylamino) phosphine oxide and a2-hydroXy-4,4-dialkoxy-benzophenone as described in U.S. Pat. 3,003,996,issued Oct. 10, 1961; a stabilizer combination comprising2,2-methylenebis(6-methylcyclohexyl-p-cresol) and a2-hydroxy-S-alkylbenzophenone as described in U.S. Pat. 3,000,856,issued Sept. 19, 1961, and a mixture of copper stearate andp-tertiarybutylphenol.

Agents which may be incorporated in the surface of polyolefin materialsinclude those which are finely-divided solids. For instance, these maybe silicas, aluminum hydroxide, talcum powder, ground glass, titaniumdioxide and the like. Various concentrations may be used and the solidmaterial may be used in the form of a dispersion. Varying degrees offineness may be used for solid materials, but colloidal size ispreferred. The incorporation of finely-divided solid material into thesurface of polyolefins improves the adhesion of coatings on thepolyolefin surface and also improves its ability to retain printing andthe like. Other agents which may be incorporated by adding to thelubricants during compression rolling, include slip agents, such asvarious polymeric materials, which can be added to the lubricatingagent. Typical of these are aliphatic and aromatic amides, preferably of12-25 carbon atoms, i.e., stearamide, or the like. Commerciallyavailable slip agents such as Armid-O may be used.

Antiblocking agents may also be added as well as moistureproofingagents. Typical antiblocking agents include diatomaceous earth, ethylenedistearamide, and the like. Typical moistureproofing agentsincludemicrocrystalline wax and paraifin wax. In many instances, theadditives which are used may accomplish more than one purpose. Forinstance, the use of talc as an additive may not only provide a slipagent or antiblocking agent but may also improve the surface so that ithas improved the adhesive properties.

Many other additives are known in the art and these can be alsoincorporated into the surface of a polymeric film in a similar manner.It would not be feasible to list every known additive, but the onesshown herein are typical of those which may be added by combining with asuitable lubricant for use in compression rolling of polyolefins. Insome instances, the additives may be prepared in the form of an emulsionand suitably added by using the emulsion as a lubricant.

Several additives may be used in combination depending upon the ultimateuse of the polyolefin sheeting.

Polymers such as polyolefins which may be further improved in theprocessing characteristics by quenching the molten polymer are firstheated to obtain a clear melt and then extruded through a suitable dieto obtain a film of the desired thickness. The film may then be quenchedby passing it into cold water or else onto a chilled cold roll so thatthe polymer is solidified and cooled rapidly during contact with thesupport to a temperature far enough below its recrystallizationtemperature to avoid clustering of crystals or excessive formation ofspherulites. The cooling liquid could be as warm as 210 F. and could becooled down to about :65 F. depending upon the melting point of thepolymer and the size of the cooling medium.

Polyolefins may be compression rolled which are substantiallycrystalline selected from those polyolefins obtained by polymerizing an(ll-Olefin having 2-10 carbon atoms or copolymers of these a-olefins.

Polyolefins which are within the scope of our invention includepolyethylene and polypropylene which are substan tially crystalline andalso blends of polyolefins, polyolefins such as poly-4-methylpentene1,poly-3-methylbutene- 1, polyallomers and related homologs.

The propylene-olefin polyallomer is a normally solid, crystallinepolymer prepared as by first polymerizing propylene to form acrystalline, propylene polymer and then copolymerizing said propylenepolymer with another orolefin having 2-10 carbon atoms until theresulting product has an olefin content of as much as by weight.

In compression rolling polyethylene, we use a polyethylene having adensity of .910 to .975 g./ cc. obtained in a sheet 2-l0 times thethickness which is desired in the finished sheet. The polyolefinsheeting is passed between rolls having a pressure sufficient todecrease the film /2 to A in thickness. The temperature of the pressurerolls depends on the density and the softening temperature of thepolyolefin; for polyethylene, the temperature preferably would be in therange of -240 F.; for polypropylene, 40285 F.; preferably l00270 F.

Various methods of heat treating the polymer sheeting may be used suchas surface winding on a take-up roll and then heating the roll in anoven. However, temperature and time relationships can be balanced, forexample, a higher temperature relaxing the film in a shorter time. Thetemperature at which the film is relaxed must be approximately the creepor distortion temperature of the particular polymer and must be lowerthan the fatigue temperature of the polymer. By fatigue temperature, asused herein, is intended the temperature at which the tensile strengthof the polymer is between 14 and 20 pounds per square inch. The creep ordistortion temperature is the temperature at which the length of a testspecimen is increased or decreased 2% of its original length, when thetest specimen is supporting a linear load of 10 grams per squaremillimeter and the temperature is being increased at the rate of 10 C.per minute.

By using a lubricant in compression rolling, we can obtain an improvedmodulus and transparency for a thicker film than can be obtained usingthe same type of polymer without a lubricant. Additional improvementsobtained by using a lubricant include a clearer film than is obtainedunder similar conditions without using a lubricant. The pressurerequired is not as high to obtain the same reduction and thickness.Moreover, static charges are reduced in the rolling operation and may becompletely eliminated. Film may be rolled flat for certain uses such aspackaging without the need for a separate step of heat treatment.Irregularities in the film thickness or gauge are not as critical whenlubricants are used as when film is rolled dry. The roll finish is notas critical for obtaining surface gloss with lubricants since scratchesor imperfections will be filled or covered by the film of lubricantwhich covers the rolls.

The rate at which the film is rolled by the pressure roll is notcritical, since satisfactory films can be produced at speeds from 2 /2feet per minute upwards to about 1700 feet per minute.

Various polymeric materials may be used in our process includingpolyesters such as polyethylene terephthalate, polyamides (nylon),polycarbonates, chlorinated polyethers, polyacetals, cellulosics, suchas cellulose acetate,

cellulose propionate, cellulose butyrate and the like, halogenatedpolyolefins such as polytetrafiuoroethylenc, etc.

Lubricants that might used would be hydrocarbon: such as xylene, VMPnaphtha, esters such as butyl acetate alcohol such as butanol, etherssuch as diethyl Cellosolve alcohol-ethers such as 2-ethoxyethanol,ketones such a: methyl-isobutyl ketonc, glycols such as ethylene anddiethylene glycol, water with and without a wetting agent paraffin orparaffin emulsions, low-molecular weight poly ethylene waxes and thelike.

The same set of rollers can be used for compressior rolling multiplestrips of polyolefin sheeting for obtaining two or more compressionrolled strips at the same time In order to compression roll multiplestrips, two 01 more sheets of the polymer are fed into the compressiorrolls having a lubricant covering the surfaces of the polymeric sheetingas it contacts the rolls at the nip. When the sheets have similarchemical compositions, the lubricant must also cover the surface of thepolymeric sheeting where it contacts another similar surface to avoidobtaining adhesion of the strips to each other. However, if the chemicalcomposition of the sheets is dissimilar enough such as polyethylenerolled with polypropylene; no lubricant is required between thedissimilar sheets.

The multiple rolling process is particularly adaptable to compressionrolling lay-flat tubing. This tubing can be prepared by methods alreadyknown in the art. However, in our preferred embodiment, the polymerictubing, such as polypropylene, is prepared by dry extruding seamlesstubing into a water bath where the tubing is inflated with a liquidhaving a higher density than water before running the tubing throughpinch rolls. The gauge of the tubing is determined by the liquid levelinside the tubing, the density of the liquid, and the draw-down betweenthe die and the pinch rolls. This process is particularly useful forpolypropylene since an improved product is obtained when the lateralstretching of the polypropylene occurs at the time it is quenched. Theprocess of compression rolling multiple strips as set forth in US. Pat.No. 3,194,863 to Williams et al.

The accompanying drawing illustrates one embodiment of our invention.

The polymer 3 in this embodiment is extruded from the extruder 1 throughthe die lip 2, onto a chilled roll 4, around the idler roller 5, throughthe tension rollers 6 and 7, and between the pressure rollers 8 and 9,at which point the polymer is reduced in thickness to nineteentwentiethsto one-tenth of the thickness as extruded. Next the polymer passesaround the idler roller 10 to relaxing roller 11 which is heated toabout 200 F., past the idler roller 12 and around the chilled roller 13to take-up 14. All the rollers are similarly supported except for thepressure roller which requires a heavy support. Lubricants are appliedthrough nozzles 15 associated with the plate 16 connected to thelubricant.

With certain of the polymer materials the polymer may be reduced toclear melt by feeding pellets of the polymer between two heated rollersuntil the polymer reaches a molten state and then passing it through aseries of rollers in a similar manner as described above. With otherssuch as the cellulose esters, polycarbonates, etc., film may be preparedby casting a dope on a polished surface.

It will be apparent to one skilled in the art that the position of therollers may be changed from horizontal to vertical and they may bearranged in various positions relative to each other, such as in the Sor Z position. The idler rollers are used to facilitate transfer of thepolymeric sheeting wihout large heat transfers from the rollers whichare maintained at certain temperatures.

The following examples are intended to illustrate our invention but notto limit it in any way:

EXAMPLE 1 The following table shows examples of polymeric materialswhich have been compression rolled according to our invention.

Roll Percent Modulus, 10 p.s.i. MIT folds Elmerdorf tear, g. temp,exten- [nple Lubricant F. sion Length Width Length Width Length Widthlyester Diethylene glycol 200 104 6. 4 2.0 2, 000+ 2,000+ 848 192llulose triacetate. Aerosol T solution. 150 6 5. 7 5. 7 46 50 48 48 D0-Paraffin emulsion l 150 23 6. 5. 5 37 58 25 23 Do- Xylene 220 12 5. 6 5.4 21 43 45 48 Do Check-not calendered 4.7 5.8 39 51 64 63 1 Paraffinemulsion-4 g. paraffin, 4 g. Aerosol OT, 500 ml. water, 200 ml.isopropanol.

EXAMPLE 2 A sheet of high density polyethylene having a density .962 g./cc. was prepared as described in Example 8 havg 60 mils thickness andalso drawn perpendicular to the rection of extrusion at 100 F. to athickness of 25 mils 40% extension). It was then pressure rolledparallel to c direction of extrusion at 240 F. to a thickness of 5 ils(400% extension). The film was wound to prevent iy elastic recovery ineither direction and heated for 30 inutes at 240 F. The modulus of thefinished film was 0 to 4.5 x pounds per square inch. The percent atteredlight was less than 3% and the creep temperare was above 240 F.

EXAMPLE 3 In the following table, results are shown for the percenttension obtained with polyolefins when rolled with EXAMPLE 4 Thefollowing table gives a comparison of properties of polyolefin filmsobtained by pressure rolling using lubricants and without lubricants.The minimum roll temperatures for obtaining the required extension withdry rolling and with lubricants was determined to eliminate the visualhaze in the original films. The samples were extruded as in Example 13.

Comparison of properties 01 polyolefin films Relaxed by lubricating anddry rolling hour 'Iernp., F. under Percent 2% di storsufiiicient MVTR, Flm total Elmention under tension to grams Roll Percent tinckscatdorfModulus p.s.i. prevent per 100 temp, extenness tered tear (10 load(reshrinkage, i )ll procedure F. sion (nnls) light (grams) p.s.i.) laxedfilm) F. 24 hrs,

Medium density polyethylene:

Lubricated (MeOH) 80 304 1- 2 1. 11 448 1.4 194 220 0 11 Dry 120 304 1.2 a. 17 17s 0. s 192 22 Phillips process hi-density polyethylene:

Lubricated (HzO/ABIOSO OT) 80 403 2. 2 2. 48 32 2, 5 237 23g 0 Dry 150392 2. 2 3. 07 4s 2. 2 232 239 0' 1 Ziegler process h1-dens1typolyethylene:

Lubricated (H O/Aerosoi 0T) 80 6 2. 2 56 16 2. 2 217 239 0 10 Dry 160are 2. 2 a. 27 1e 2. 2 223 239 13 Polypropylene: I

Lubricated (ethylene glycol) 200 376 3 8 16 2- 9 266 284 0 25 Dry 240377 2. 2 a. 49 1e 3. 4 246 284 24 1 MVTR represents Moisture VaporTransmission Rate.

Norm-All physical ed light and MVTR.

lubricant and without a lubricant. Methanol was used as e lubricant forpolyethylene; ethylene glycol was used r polypropylene.

The minimum percent extension using a lubricant was termined which wasrequired to eliminate the visual haze the original films. The pressurerequired to obtain the inimum percent extension using a lubricant whichminated visual haze was determined for each resin. lms were thencompression rolled with and without bricant at these pressures. Rolltemperatures were 80 for polyethylene and 200F. for polypropylene. Eachmple was extruded from a clear melt. One and three :re extruded onto achilled roll. Two and four were truded into a quench hath.

Percent extension Various additives which are soluble in methanol andiylene glycol are added to the lubricant prior to the mpression rolling.The amount of additive varies dending upon the viscosity of thelubricant but sufiicient properties in the above table were determinedon films in the direction parallel to that of extension by rollingexcept for seat- EXAMPLE 5 Haze and extension determinations as followswere made on medium density polyethylene (0.93 g./ cc. Films werepressure rolled at a roll temperature F. using film extruded from aclear melt onto a chilled roll.

Mils Percent Percent total for medium density polyethylene (0.93 g./cc.)extruded as in Example 5.

t Roll Thickuesls Pcrcen t emperaori ina exten- Lubrieant ture mils'sion Isopropyl alcohol 80 Petroleum oil 80 Methyl ethyl ketone 80 30 310Cyolohexane 80 30 376 1,2,3,4-tetrahydronapthalene. 8U 30 388 Methylalcohol 80 30 350 9 EXAMPLE 7 The following determinations show therelationship between polyethylene samples of varying densities ofsamples pressure rolled using methyl alcohol as a lubricant. Thepolyethylene was extruded as in Example with no appreciable drawdown andthe samples were not heat treated.

Haze, Modulus 100 in /24 Density percent Thickness above hrs All-.929 32.5 1.0X .20

EXAMPLE 7A Length Width Tensile strength at break, 1bS./sq. in. 13, 70015, 200 Elongation at break, percent 20.2 24. 3 Modulus, lbs/sq. in 3.5X10 3.5)(10 Elmendorl tear, g 23 26 Haze 2. 0 2.0

EXAMPLE 8 A propylene polyallomer containing ethylene and having adensity of 0.906 g./cc. and a flow rate of 1.38 at 230 C. using a 2160g. load was extruded from a 1 /2 Modern Plastics extruder as five milstrip. The melt temperature of the polyallomer entering the die of theex- 1 0 EXAMPLE 9 A propylene polyallomer containing butene-l having adensity of 0.913 g./cc. and a flow rate of 2.0 at 230 C. using a 2160 g.load was extruded as strip. This polyallomer was extruded at a melttemperature of 223 C. into a 24 C. Water bath as strip 5.9 mil thick.The strip was compression rolled between polished steel rolls heated to127 C. using a 10% ethylene glycol/ 90% water lubricant to 1.3 mil film.

Physical properties determined on the compression rolled film were:

Moisture vapor transmission (grams/ 100 sq. in./

24 hr.) 0.40 Lemon oil permeability (grams/ 100 sq. in./24

hr.) 1.44 Percent haze 2.32 MIT folds:

Length 500+ Width 500+ Tensile at yield, 10 p.s.i.:

Length 35.0 Width 5.3 Elongation at yield percent:

Length 38 Width 4.8 Modulus, 10 p.s.i.:

Length 4.8 Width 2.4

EXAMPLE 10 Blends were prepared of a high density polyethylene resinhaving a density of 0.96 g./cc. and a low density polyethylene resinhaving a density of 0.925 g./cc. by mechanically mixing the pellets ofthe compositions prior to extruding. These blends were extruded as striponto a chill roll, then compression rolled in a two-roll Fenn Mill usinga .03% Aerosol OT/water solution as the lubricant. Conditions forrolling and physical properties truder was 225 C. The lips of theextruder die were set 40 determined on the compression rolled filmswere:

Composition, percent High Low Modulus, Moisture density density RollPercent 10 p.s.i. vapor, transpolyethpolyethtemp, mission g./ yleneylene 0. Roll down Haze Length Width 100 in./-24 hr.

20 mils apart and the strip was drawn down to 5.6 mil EXAMPLE 11 beforebeing quenched in a 24 C. water bath located four inches from theextruder die lips. The extruded and quenched strip was compressionrolled using a 10% ethylene glycol/90% water lubricant between polishedsteel rolls heated to 127 C. The thickness of the strip after one passbetween the rolls was 1.2 mil. Physical properties determined on thefilm after compression rolling were:

Moisture vapor transmission (grams/1 00 sq. in./

A strip of polyethylene terephthalate was extruded and quenched toproduce an amorphous structure. The amorphous strip was tentered to 3times its original width then compression rolled to 3.5 times itsoriginal length. The tentered strip was compression rolled at 127 C.using a 20% ethylene glycol/ water lubricant. Modulus values determinedin three directions were:

Direction of sample: Modulus, 10 p.s.i.

Length (compression rolling direction) 6.6 Width (tentering direction)6.1 Diagonal (45 to length and width) 6.2

This balance in modulus between the length, width and diagonal is asignificant improvement over the balance found in films of thiscomposition oriented by conventional tentering and drafting procedures.Attempts to compression roll this film without a lubricant but at thesame roll temperature and pressure resulted in less than 30% extensionin the length of the strip.

EXAMPLE 12 A polycarbonate resin having an intrinsic viscosity of 1.12in methylene chloride at 25 C. was plate coated as a film from a1,1,2-trichloroethane dope of the resin. X-ray flraction patterns of thecured film indicated the strucire was crystalline. Percent haze of thefilm as cured as 27.3. This film was compression rolled from a thick-:ss of 4 mils to 2 mils between rolls heated to 104 C. ;ing a 0.03%Aerosol OT/ water lubricant. Percent haze f the compression rolled filmwas 6.0.

EXAMPLE 13 A polycarbonate resin (intrinsic viscosity in methyleneiloride of 1.45) plasticized with parts triphenyl-phosrate was coated ona coating wheel from a methylene iloride dope. The coated and cured filmwas 5.4 mils .ick and the percent haze was 21.4. This film was comessionrolled to a thickness of 3.45 mils between rolls :ated to 110 C. usingethylene glycol as a lubricant. :rcent haze of the compression rolledfilm was 5.5.

EXAMPLE 14 A melt of polyhexamethylene adipamide was extruded om a 1 /2inch Modern Plastic extruder as five mil m. The take-off equipment forremoving the film as it as extruded was a water tank and a Fenn Millcompreson roll assembly. The tank was filled with a water ienching bath.Thus, the extruded five mil film of poly- :xamethylene adipamide enteredthe water bath where was quenched and then was fed directly from thebath to the nip between the two 10 inch diameter polished eel rolls ofthe Penn Mill and reduced in thickness to 6-2.0 mils. The percent hazedetermined on the film 'ter compression rolling was in excess of 12.

It is believed that the poor haze factor possessed by e compressionrolled polyhexamethylene adip-amide m is directly attributed in largemeasure to the fact at the film was not evenly covered by the watercarried ereon. A visual inspection of the polyhexamethylene liparnidefilm leaving the water bath and entering the mpression roll assemblyrevealed that the water tended puddle or otherwise run off the filmprior to its aching the roller nip.

EXAMPLE 15 A melt of polyhexamethylene adipamide was extruded om a 1 /2inch Modern Plastic extruder as five mil film. he take-off equipment forremoving the film as it was Lt1'\1dd was a roll take-up assembly. Thus,the extruded e mil film of polyhexamethylene adipamide was solidi- :ldwhile being conveyed through room temperature air id was then wound. Thewound polyhexamethylene adipnide was then compression rolled between thetwo 10 /2 ch diameter polished steel rolls of a Penn Mill to a icknessof 1.5-1.6 mils. A standard Stoddard solvent is placed on both surfacesof the five mil film just 'ior to its entering the nip of the rolls.Since the Stoddard lvent is not absorbed by the polyhexamethyleneadipnide film but rather spreads evenly over the surface of e film, itacts as a lubricant within the meaning of e term as used in thisinvention. The percent haze of e film that had been compression rolledwith Stoddard lvent as a lubricant was 0.9-1.0.

Thus, by comparing the results of this example with at obtained underthe conditions set out in Example i, it can be seen that acceptableresults can be obtained ily when the film is evenly covered with alubricant.

EXAMPLE 16 A section of the roll of five mil polyhexamethylene lipamidefilm that had been extruded into air and wound the manner set forth inExample 15 was compression lled in the Fenn Mill, and reduced inthickness to 1.6- 7 mils using Aerosol OT/ water lubricant applied toboth les of the film. The percent haze determined on the y filmcompression rolled with the Aerosol OT/water rface lubricant was 2.6.

EXAMPLE 17 A hygroscopic polymer in the form of nylon was soaked l 12 inwater for 24 hours at F. After being removed from the water bath, thesurface of the sheet was wiped free of surface water and weighed. Thegain in weight determined was 7.47%. A similar sheet of polyethylene wasalso soaked in water for the same period of time under the sameconditions. The gain in weight was 0.03%.

Sheets of nylon were compression rolled using water as a lubricant. Thepolymeric sheets had not been soaked in water and the lubricant wasapplied to the surface of the sheets at the point of pressure betweenthe compression rolls.

The following table shows the comparison between the compression-rollingoperation using a lubricant and compression rolling the film directlyafter soaking in water for 24 hours:

The roll pressure used with all the samples was the maximum that couldbe obtained on a No. 102 Fenn Mill equipped with rolls 10 inches indiameter. These results illustrate the difference in the efiect ofinternal plasticization and surface lubrication on compression rollingof nylon.

EXAMPLE 18 Spencer type 401 nylon was extruded from a 1% inch ModernPlastic extruder as five mil film. The take-off equipment for removingthe film as it was extruded was a tank and roll assembly. The tank wasfilled with 60 F. water until it was within six inches of the extruderdie lips. A roll of film was then extruded and left submergedin the tankfilled 'With water for twenty-four hours. After the fihn was soaked fortwenty-four hours, it was removed from the tank taking all possibleprecautions to prevent removing any water that adhered to the surface ofthe film. This soaked film was compression rolled immediately afterremoval from the tank between two 10 /2 inch diameter polished steelrolls in a Penn Mill and reduced in thickness to 1.5-1.6 mils. Thepercent haze ge7termined on the film after compression rolling was Thusit is readily seen that the same haze factor is produced in a nylon filmwhether its surface has all the water thereon that it will carry, as isthe case in this example, or is wiped dry as was done in Example 17.Therefore, it is apparent that the polyamide is plasticized bysaturating it with water and that the water cannot function as alubricant during compression rolling.

EXAMPLE 19' A commercially-obtained sheet of polystyrene having anaverage thickness of 5.0 mils was compression rolled satisfactorilyusing a lubricant. The following data were obtained:

Roll

EXAMPLE 20 A commercially-obtained sheet of polytetrafluoroethylenehaving an average thickness of 5.0 mils was compression rolledsatisfactorily using a lubricant. The following data were obtained:

R011 temp, Pressure Percent Polymer Lubricant F. lbs. extensionPolytctrafiuoro- None. 170 2,000 95 ethylene.

03% aeorsol/HgO 170 2,000 113 10% glycol/90% H 170 2,000 127 Toluene 1702,000 125 Silicone 170 2,000 120 EXAMPLE 21 A sheet of cellulose acetatebutyrate was prepared by extruding the cellulose acetate butyrate from aclear melt to form a sheet having an average thickness of 4.6 mils. Thesheet was satisfactorily compression rolled using a lubricant with theresults disclosed in the following table:

A polyacetal polymer resin obtained commercially [under the name Delrin]was extruded to form a sheet having an average thickness of 38 mils.This material was satisfactorily compression rolled as shown in thefollowing table:

Roll Pres- Percent temp, sure, exten- Polymer Lubricant 1*. lbs. sionPolyacetal None 200 18, 000 182 03% aerosol/H2O. 200 15,000 469 EXAMPLE23 A commercially-obtained sheet of polyvinyl chloride having an averagethickness of 10.1 mils was compression rolled satisfactorily using alubricant. The following data were obtained:

Roll Pres- Percent temp, sure, exten- Polymer Lubricant F lbs. sionPolyvinyl chl0ride. None 200 5,000 83 H2 155 6,000 116 03% ac Sol/H 175l 9, 000 116 do 165 9, 000 102 do 155 6, 000 124 125 5, 000 102 octylphtha- 200 5, 000 88 late/90% isopropanol) lvlaximurn.

EXAMPLE 24.-ANTIOXIDANTS Strips of unstabilized polypropylene werecompression rolled from 24 mils to 8 mils thickness at a rolltemperature of 200 F. After 42 hours under an ultraviolet lamp, a dryrolled strip had an inherent viscosity in tetralin of 0.50. A striprolled with an isopropanol lubricant containing 8% 4,4thiobis(6-te-rtiary butyl 3-methyl phenol) had an inherent viscosity of1.31 after the same exposure.

14 EXAMPLE 25.ANTIBLOCKING AGENTS An extruded polypropylene strip wasdry rolled from 20 mils to 5.5 mils at a roll temperature of 200 F; astrip of the same thickness was rolled to 5.0 mils using an isopropanollubricant containing 24% Armid O (oleamide). A block test similar toASTM 884-48, in which the samples were heated 16 hours at 81 C. under a5 psi. load, rated the dry rolled sample as blocking badly and thelubricated sample with Arrnid O (oleamide) as no block.

EXAMPLE 26.ANTIBLOCKING AGENTS An extruded polypropylene strip was dryrolled from 20 mils to 5.5 mils at a roll temperature of 200 F.; a stripof the same thickness was rolled to 5.0 mils using an isopropanollubricant containing diatomaceous earth in dispersion. A block test inwhich the samples were placed under a 1.0 p.s.i. load for 380 hours atroom temperature rated the dry rolled sample as blocking and thelubricated sample with diatomaceous earth as no block.

EXAMPLE 27.-1SLIP AGENTS The rolled strips of Example 25 were subjectedto a slip test that measured the force in grams necessary to slide thesample across itself. A slip test result of 15 was obtained on the dryrolled sample and 7 on the sample rolled with Armid O (oleamide) inisopropanol.

EXAMPLE 28 Various additives including stabilizers, inhibitors, slipagents, antiblocking agents, surface modifiers, moisture proofing agentsand the like are incorporated in the lubricants and the polyolefinsshown in the above examples compression rolled and stress set to obtaintransparent polymeric films. The haze measurements as expressed inpercent total scattered light are in no way changed significantly due tothe presence of the incorporated additives, nor are the othercharacteristics such as the percent extension, tear strength, modulus ormoisture vapor transmission aifected adversely by the incorporation ofthe additives in the lubricant.

EXAMPLE 29' Haze and extension determinations as follows were made onmedium density polyethylene (0.93 gram per cc). Films Were compressionrolled at a roll temperature of F. using film extruded from a clear meltonto a chilled roll.

Thickness Percent Original after thickness, rolling, Exten- ScatteredLubricant m s mils sion ligh 4. 5-5. 0 1. 0-1. 5 280 1. 57 4. 5 5. 0 1.0-1. 5 217 3. 20 4. 55. 0 1. 0-1. 5 217 3. 44 Buty1alc0h0l 4. 5-5. 0 1.0-1. 5 217 1. Water with wetting agent 4. 5-5. 0 1. 0-1. 5 217 2. 13Methyl alcohol 4. 5-5. 0 1. 0-1. 5 217 1. 60

When additives are incorporated in a lubricant sufliciently to improvethe surface, to stabilize and to inhibit the polyolefin, the percentscattered light is found to remain substantially the same.

EXAMPLE 3 0- Maximum extension values were determined as follows frommedium density polyethylene (0.93 gram per cc.) extruded as in Example29.

Original thickness Percent Lubricant Roll temp. mils extension Isopropylalcohol. 80 30 322 Petroleum oil .z 80 30 325 Methyl ethyl ketone 80 30310 Cyclohexane 80 30 376 123,4 tetrahydronapthalenm-, 80 30 388Whenever additives such as stabilizers and inhibitors e incorporated inthe lubricants sufficient to incorporate out OBI-1.0% by weight of theadditive, the physical operties of the polyolefin are the same as whenthe mples are compression rolled using the lubricants withit having theincorporated additives.

The crystalline structure of the film may be determined 1 X-raydiffraction patterns as is well known in the art. the event thatstretching is desirable, the polymeric film ay be stretched in adirection laterally perpendicular the direction in which the compressionrolling takes ace. The stretching step may be carried out using cusmarytentering equipment or it may be obtained by exiding plastic tubingwhich is extended laterally by using the tubing to be filled with afluid such as air, 11:61 or the like. In one embodiment of ourinvention, the rlymer is extruded as a tubing into a water bath andetched by having a liquid contained inside the tubing, rich ispreferably of greater density than the water.

A roll stack may be used which would eliminate the .truder where pelletsare used which are converted into In by masticating rolls, then rolleddown and relaxed on ccessive rolls in the stacks.

The pressure rolls have a pressure of at least 100 iunds per linear inchdepending upon the polymer meased along the line where the sheetingpasses between e two rolls. In other words, if 6-inch long rolls wereed, the pressure exerted by the rolls, if the pressure were pounds perlinear inch, would be 1,800 pounds total essure exerted by the rolls. Inthe event that the polyeric film is an amorphous polyester, it may bestretched one direction at temperatures of 70-105 C. and then lled in adirection substantially at right angles to the rection of stretch in arolling mill at temperatures of l() C. using a lubricant. The film maythen be heatt at a temperature of l50-250 C. while shrinkage of e filmin any direction is prevented by maintaining the or under tension in thetwo directions.

Instead of a step requiring stretching in one direction, e polymericfilm may be rolled in two directions by ssing the film through thepressure rollers in a direction bstantially diagonally so that thepressure rolling can be tained in directions substantially perpendicularto each her. For small sections, however, the film may be lled in onedirection and then a section removed for lling in a transversedirection.

A satisfactory method for measuring the second-order tnsitiontemperature is dependent upon the change in e specific heat of thepolymer at that temperature. If a lymer is heated at a constant ratebeginning at a temrature below its second-order transition temperature,a temperature will increase at a constant rate until the msitiontemperature is reached, at which point a break the curve will occur. Thedeterminations are made by icing the insoluble polymer with eithernormal-heptane toluene at a temperature around 60 C. in a calorim- :r. Aconstant rate of heating is obtained using an eleccal heater connectedto a voltage source which may be ried at will. The powdered polymer iskept suspended an electric stirrer turning at constant speed. Temperareis measured by means of a copper-constantan thermouple with an ice waterreference point. After the lorimeter has reached equilibrium, thecurrent is rned on so that the temperature will rise about 1 C. perinute. The zero time reading is selected at least C. low transitiontemperature. Thereafter, the lapse time read off a stop watch to thenearest of a minute for ery degree centigrade rise. After going l0=20 C.higher an the inflection point, as noted by the data, the inrmation isplotted on the graph.

The polyethylene or similar polymer may be used rect from thepolymerization autoclave in the melt rm to make sheeting and thencompression rolled. Cellulose esters and other highly crystallinepolymers I not require a high percentage extension. Possibly 16 5%extension would be sufiicient to provide orientation.

This procedure could be modified to extrude the film directly into thenip of the pressure rolls and quench the film with the lubricant at theinstant the sheet contacts the rolls at the nip. This variation would bemost effective for fabricating films of polymers which cannot bequenched to amorphous structures by practical procedures. The melts ofsuch polymers are essentially amorphous but recrystallize readily whencooled and frequently become translucent or opaque over a narrowtemperature range, which will be referred to as the frostline. A sheetof such polymers could be extruded as a clear melt directly into the nipof the pressure rolls which would be flooded with lubricant maintainedat the frost-line temperature. Orientation and crystallization wouldoccur simultaneously in this process which is the preferred sequence formost polymers. This would also make possible the fabrication of thingauge films without draw-down or extension by drafting.

From the foregoing it is apparent that the use of a lubricant film on apolyethylene sheet as it is being rolled results in the sheet undergoinga substantially larger percent extension than can be produced if thesheet is rolled without a lubricant. It is also of major importance thatthe use of such a lubricant permits an extremely thin finished sheet tobe produced in one pass through the rolls with substantially less rollpressure than was heretofore thought possible. However, perhaps the mostsurprising and important feature of this invention is the opticalclarity of the finished film. Thus, this invention which teaches how alimp and cloudy polyolefin sheet material can be transformed in one passthrough a low pressure compression roll into a thin, crisp, ultra-clearsheeting through the use of a lubricant on both sides of the sheetrepresents a substantial step forward in the polyolefin sheeting field.

What is claimed is:

1. A transparent [polyolefin] polyethylene film having a modulus above1.0 10 pounds per square inch and a haze value of less than 3%.

2. A transparent [polyolefin] polyethylene film according to claim 1wherein said [polyolefin] polyethylene is medium density polyethylenehaving a density of from 0.93 to 0.945 and its modulus is above 2.0 l0pounds per square inch.

3. A transparent [polyolefin] polyethylene film according to claim 1wherein said [polyolefin] polyethylene is high density polyethylenehaving a density of from 0.946 to 0.97 and its modulus is above 25x10pounds per square inch.

4. A transparent low density polyethylene film having a density of from0.91 to 0.929 and a modulus above 1.0)(10 pounds per square inch, a hazevalue of less than 3%, and which at a thickness of 2.5 mils have amoisture vapor transmission rate of about .20 gram per square inches ofsurface in a 24 hour period.

5. A transparent medium density polyethylene film having a density offrom 0.93 to 0.945 and a modulus above 211x10 pounds per square inch, ahaze value of less than 3%, and which at a thickness of 2.5 mils has amoisture vapor transmission rate of about .15 gram per 100 square inchesof surface in a 24 hour period.

6. A transparent high density polyethylene film having a density of0.946 to 0.97 and a modulus above 2.5)(10 pounds per square inch, a hazevalue of less than 3%, and which at a thickness of 2.5 mils has amoisture vapor transmission rate of about .10 gram per 100 square inchesof surface in a 24 hour period.

7. A polypropylene film having a modulus [at] of about 3.5 l0 pounds persquare inch in its lengthwise direction, a modulus of about [3.5] 3.5 10pounds per square inch in its widthwise direction, and a haze value ofless than 3%.

8. A transparent polypropylene film having a modulus UNITED STATESPATENTS above about 1.7 X10 pounds per square inch in the 3 194 3 9 5Williams 1 et aL widthwise direction and above about 3.3 X10 pounds per264-175 X square inch in the lengthwise direction and a haze value3,037,862 6/ 1962 Neth 11734 X f l h 3%, 5 2,367,173 1/1945 Martin264-210 2,631,954 3/1953 Bright 264-175 X References Cited PHILIP DIER,Primary Examiner The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original 10 CL patent.117-34, 138.8; 161-247, 402, 411; 264-175, 210

